Automatic defrost control



Feb. 2, 1954 c; s. GRIMSHAW AUTOMATIC DEFROST coumor.

Filed Dec. 19, 1951 T244 I nvenbcr Charles S. Grimshaw,

by M

His Attorney.

Patented Feb. 2, 1954 AUTOMATIC DEFROST CONTROL Charles S. Grimshaw, Erie, Pa., assignor to General Electric Company, a corporation of New York Application December 19, 1951, Serial No. 262,447

13 Claims. 1

My invention relates to defrosting apparatus and, more particularly, to controls for automatically effecting defrosting of refrigerator evaporators.

In many household refrigerators, th evaporator for cooling the food storage compartment is exposed to the air in this compartment. Since the evaporator is at a colder temperature than the air, and below the freezing point of water, moisture condenses on the evaporator and forms as frost. Ultimately, in order to maintain the desired operating efiiciency of the evaporator, it is necessary to remove the insulating layer of frost. Since the removal of this frost manually is a somewhat distasteful and time-consuming task, it is desirable to provide some automatic means for effecting the defrosting of the evaporator at intervals.

Accordingly, it is an object of my invention to provide an improved control for automatically effecting defrosting of an evaporator.

It is another object of my invention to provide an improved control for automatically introducing an additional opposing force for defrosting.

It is a further object of my invention to provide an improved arrangement for starting refrigeration at the expiration of the defrosting period.

Further objects and advantages of my invention will become apparent as the following description proceeds, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

In carrying out the objects of my invention, a pivoted interfering member is provided for opposing movement of the operating arm of the control to a refrigeration-starting position when defrosting is to be accomplished. The interfering member is adapted to be pivotally moved between one position in which it opposes movement of the operating arm, and a second position in which it has no effect on movement of this arm. A latch is provided for engaging th pivoted member to move the member to the opposing position, and the position of this latch is governed by a cam. Movement of the interfering member in the defrost position is-opposed by a defrost spring. The member is shifted after a predetermined amount of movement against the bias of the defrost spring into a position wherein the latch is released, and a second spring then moves the member to the position it occupies during normal operation of the control.

. For a better understanding of my invention, reference may be had to the accompanying drawing in which Fig. l is a sectional plan View, taken along the lines l-l in Fig. 2, of a control incorporating an embodiment of my invention; Fig. 2 is a sectional elevation view of the control; Fig. 3 is a sectional view taken along the line 33 in Fig. 2; Fig. 4 is a sectional elevation view of a portion of the control illustrated in Fig. 2, with the parts in a different position; and Figs. 5 and 6 are views similar to Fig. 4 with the parts in still other positions.

Referring to the drawing, the control is shown applied to controlling the position of a valve l for governing flow of refrigerant from a conduit 2 to a conduit 3. Refrigerant is supplied through conduit 3 to an evaporator or other cooling unit (not shown). The valve I includes a valve plunger 4 adapted to engage a valve seat 5. A magnet 8 is secured to the upper end of the plunger 4, and the position of this magnet and of the plunger is controlled by a movable yoke l acting on the magnet. While in the specific illustration the control has been shown acting to control the position of the valve for governing the flow of refrigerant to an evaporator or other cooling unit, it will be apparent as the following description proceeds that this control can equally well be employed for opening and closing contacts to stop and start a refrigerating unit in the conventional manner employed in such controls.

The valve-controlling yoke l is mounted on one end of a two-part operating arm 8. This operating arm 8 includes a first part or element 9, and a second part or element It. These parts are related by a hairpin over-center spring II, knife edges 1': and 13 of these parts of the arm 8 engaging opposite sides of the hairpin spring H. This construction of the operating arm 8 including the hairpin spring H is employed to secure snap action operation in a manner well-known in the art. The first part 9 of the operating arm 8 is pivotally mounted between upstanding projections l4 secured to or formed integral with the housing iii of the control. The second part I!) of the operating arm 8 is supported by two brackets IE which are secured to the bottom wall of the housing I5. The part Ill is connected to the brackets l6 by fiat resilient strips I! which afford the necessary movement of the part II] of the operating arm 8.

In order to effect movement of the operating arm 8 between one position for opening the valve to start refrigeration and a second position for closing the valve to stop refrigeration, a temperature-responsive element or bellows I8 is mounted on the housing l5. The bellows i8 is connected by a tube [9 to a thermostatic bulb (not shown) positioned to be responsive to the temperature of the evaporator. The operating arm d is biased by a spring 20 which engages the part a of the operating arm 8. A cap 2! is provided for the upper end of the spring 26 and an adjusting screw 22 having an external knob 23 is threaded into the Wall of the housing l and engages the cap 2| for varying the biasing force exerted by the spring 28 to vary the maximum and minimum temperatures maintained during normal operation. The part 9 of the operating arm 8 includes an upwardly extending boss 23a, for assisting in positioning the lower end of the spring 2t.

Under normal operating conditions, i. e., during normal cycling of the refrigerating system, the movement of the operating arm 8 and hence the position of the valve I is controlled by the expansion and contraction of the bellows it under the biasing force of the opposing spring 28. For example, in the position of the apparatus shown in Fig. 2, the yoke l is in its lower position, attracting the magnet 6 upwardly and lifting the valve plunger to supply refrigerant to the evaporator. As the temperature of the evaporator is lowered, bellows l8 contracts and the part 9 of the operating arm 8 is moved downwardly by the spring 20. This effects a downward movement of the knife edge l2, eventually bringing this knife edge I2 below a line extending through the knife edge 13 and the pivot point of the part iii of the arm 8. Then through the action of the hairpin spring II, a snap-action upward movement of the part of the operating arm 3 is effected. This shifts the yoke l to the upper position attracting the magnet E downwardly to close the valve and to discontinue supply of refrigeration. Conversely, as the evaporator then warms up to a predetermined maximum temperature, the bellows I8 expands and raises the part 9 of the operating arm 8. When the part 9 has moved sufficiently to bring the knife edge l2 above a line extending through the knife edge l3 and the pivot point of the part Id of the arm 3, a snap-action movement of the yoke l to its lower position, shown in Fig. 2, is effected, thereby again opening the valve l and starting refrigeration.

During normal operation of the control, the control cycles between the refrigeration-starting and refrigeration-stopping positions in the manner described above. After a number of such cycles over a period of time, frost builds up on the evaporator to a sufiicient extent to have an adverse effect on the efficiency of the evaporator in effecting cooling of the air in which it is disposed. In accordance with my invention, after a predetermined number of such normal cycles of the control, the control is automatically positioned for efiecting a temporary abnormally high temperature of the evaporator sufficient to insure melting of the frost from the evaporator. In order to effect such defrosting an elongated pivoted interfering member 24 is provided for opposing upward movement of the part 9 of the operating arm 8, and consequently opposing downward movement of the part ii] of this arm, until the evaporator has reached a predetermined abnormally high temperature. The member 2 2 extends through an opening 25 in the upper wall of the housing l5. This member 2% includes a transversely extending section 28 having knife edges 2'! on the lower edge thereof for pivotal engagement with the wall of the housing 15. The

member 24 is arranged for movement between one position, as shown in Fig. 4, wherein this member opposes upward movement of the part 9 of the operating arm 8, and a second position, as illustrated in Fig. 2, wherein the member 2 has no effect on the upward movement of the part of the operating arm 8 to the valve-opening position. In the second position the member is aligned with an opening 24a in the part d, so that part e may move upwardly without interference by the member 2 2. In order to limit the movement of the arm 21% toward these two extreme positions, a bracket 28 is provided. This bracket 28 is secured to the upper wall of the housing it at 2:3, and includes an opening 38 therein through which the pivoted interfering member 24 extends. The bracket 28 provides a stop ii at one side of this opening 35 for limiting the movement of the arm 24 to the left in the position shown in Fig. 4.

The bracket further includes a second stop 32 at the opposite side of this opening for limiting the movement of the member 24 to the right in the position shown in Figs. 2 and 6.

For opposing the movement of the operating arm 8 to eifect the abnormally high defrosting temperature, a defrost spring 313 is provided for exerting an additional biasing force against the member 26. The spring 33 is mounted between a lower cup M and an upper cap 35. The upper end of the member 2 engages the lower cup 34. In order to vary the biasing force exerted by the spring 33 to adjust the abnormally high defrosting temperature, an adjustable screw 3'! is threaded. into engagement with a cover secured to the housing 15, and the lower end of the screw 31 engages the upper cap 35. With the pivoted interfering member 24 in the defrosting position, as illustrated in Fig. 4, the upward movement of the part 9 of the operating arm S under the influence of the expanding bellows ii! is opposed by the defrost spring 33 whose is in line with the elongated pivoted member 2A.

In order to move the member 24 from the position shown in Figs. 2 and 6 to the position shown in Fig. 4, a resilient latch 39 is provided. The latch 39 includes a generally vertical leg 40, which extends through an opening 4| in the upper wall of the housing It. The upper end. of the leg 4!] of the latch 39 is secured in any suitable manner, as by welding, to the cover 38. The latch 39 further includes a horizontally extending leg 42 which is adapted to extend through an opening 33 in the member 24. At its extremity, the leg 42 of the latch 39 includes an upwardly extending portion or hook 44 which is adapted to engage one side 45 of the member 25 for moving the member 24 toward the position shown in Fig. 4 and for maintaining it in this position. The member 24 is biased to the position shown in Figs. 2 and 6, that is, to the position it occupies under normal operating conditions, by a spring it. One end of the spring it engages a vertical wall of the bracket 28, and the other end of the spring is received within a cap 47 having a projection :38 which is received Within a recess 49 in the member 24.

The latch 39 is biased by its natural resilience to assume the position shown in Fig. 4. In order to shift the latch for engagement with the member 2d, and to control the position of the latch, a cam 55' is provided. This cam is mounted on a shaft 5| which is supported in vertical walls of the housing l5. The surface of the cam 50 is arranged to engage the vertical leg 40 of the latch 39 and rotation of the cam in the direction indicated by the arrow effects a progressive shifting of the latch to the right. The rotation of the cam may be effected in any of a number of ways well-known in the art, for example, by a timer, by a ratchetin device, etc. The cam has been shown only generally since the specific arrangement for moving it forms no part of this invention.

The parts are shown in Fig. 6 in the position occupied after a defrost period has been completed and normal operation has begun. The member 24 engages the stop 32 of the bracket 28 and, in this position it has no effect in opposing movement of the operating arm 8 to the refrigerant-starting position. As the cam is rotated in a clockwise direction, the leg d2 of the latch 39 is moved progressively to the right. During such movement, the end of this leg 42, including the hook 44, moves through the opening 43 in the member 2 2, eventually reachin the position shown in Fig. 2. As the cam 59 moves from the position shown in Fig. 2 to that shown in Fig. 4, the latch 39 rides over the tip d2 of the cam, and the latch is then carried by its natural resilience to the position shown in Fig. 4. During this movement of the latch, the hook 44 thereof engages the side 45 of the member 24 and pulls the member 24 from its inclined position, as shown in Fig. 2, to the vertical position shown in Fig. 4. It will be noted by reference to Fig. 2 that this movement of the member 24 takes place after the part 9 of the arm 8 has moved downwardly sufficiently for the member 24 to be out of the opening 24a and to clear the top surface of part 9. In the position shown in Fig. 4, the

member 24 is aligned with the axis of the spring 33 and upward movement of the part 9 of the operating arm 3 to the valve closing position can be effected only by a corresponding upward movement of the member 24 against the additional bias offered by the defrost spring 33. Hence, a greater force must be exerted by the bellows l8 and, therefore, a higher temperature of the evaporator or cooling unit to which the bellows is responsive is required.

As the bellows expands and the member 24 is moved upwardly from the position shown in Fig. 4, the opening 13 in the member 24 is ultimately moved into horizontal alignment with the upwardly extending hook M of the latch 39. Upward movement of the leg 42 of the latch 39 and hence upward movement of the hook d4 thereof is prevented by the lower end 53 of the stop 3i. At a predetermined abnormally high temperature, the opening ca moves into horizontal alignment with the hook i so that the hools M is able to pass through this opening. The latch 355 is then retracted to the position illustrated in Fig. 5 wherein the hook id of the latch is disposed within the opening 43". At this same time or shortly thereafter, a part 9 of the operating arm 8 has been moved upwardly to a sufficient extent by the expansion of the bellows it that the knife edge i2 is above a line extending through the knife edge !3 and the pivot point of the part it of the arm 3. This effects a snap-action movement of the yoke l to its lower position, opening the valve i.

At this time, the member 2 still held in its vertical position, as shown in Fig. 5, by the friction of this member against the part 9 of the operating arm 8. As the evaporator cools after the termination of the defrosting period, the bellows l8 contracts and the part 9 of the operating arm 8 is moved downwardly by the spring 20 to reduce this frictional restraint on the lower end of the member 24. When this frictional restraint is sufliciently reduced, the member 24 is shifted to the position shown in Fig. 6 by the action of the biasing spring 48 which exerts a force tending to move the member 24 in a counter-clockwise direction about the knife edges 2?. Normal operation of the refrigerating system is then resumed and continues until the cam has rotated sufficiently that the latch 39 again rides over the tip 52 of the cam, again moving the parts to the position shown in Fig. 4.

While I have shown and described a specific embodiment of my invention, I do not desire my invention to be limited to the particular construction shown and described and I intend by the appended claims to cover all modifications within the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A refrigerator control comprising a pivoted operating arm movable between two positions for starting and stopping refrigeration at predetermined maximum and minimum temperatures, a temperature-responsive element engaging said arm for effecting movement thereof, a biasing spring engaging said arm for opposing said element, an interfering member movable between a first position wherein said member opposes movement of said arm and a second position wherein said member does not oppose movement of said arm, a latch for engaging said member, means for moving said latch to shift said mem her to its first position, and means for biasing said member toward its second position.

2. A refrigerator control comprising a pivoted operating arm movable between two positions for starting and stopping refrigeration at predetermined maximum and minimum temperatures, a temperature-responsive element engaging said arm for effecting movement thereof, a biasing spring engaging said arm for opposing said element, an interfering member movable between a first positionwherein said member opposes movement of said arm and a second position wherein said member does not oppose movement of said arm, a latch for engaging said member, a cam engaging said latch for affording movement of said latch to shift said member to its first position, and means for biasin said member toward its second position.

3. A refrigerator control comprising a pivoted operating arm movable between two positions for starting and stopping refrigeration at predetermined maximum and minimum tempera tures, a temperature-responsive element engaging said arm for effecting movement thereof, a biasing spring engaging said arm for opposing said element, a pivoted interfering member movable between a first position wherein said member opposes movement of said arm and a second position wherein said member does not oppose movement of said arm, a latch for engaging said member, a cam engaging said latch for affording movement of said latch to shift said member to its first position, and means for biasing said member toward its second position.

4. A refrigerator control comprising a pivoted operating arm movable between two positions for starting and stopping refrigeration at predetermined maximum and minimum temperatures, a temperature-responsive element engaging said arm for effecting movement thereof, a biasing spring engaging said arm for opposing said element, a pivoted interfering member movable between a first position wherein said member opposes movement of said arm and a second position wherein said member does not oppose movement of said arm, a latch for engaging said member, said member having an opening theresaid latch being adapted to extend through said opening, said latch including a portion for engaging said member, a cam engaging said latch for affording movement of said latch and said portion thereof to shift said member to its first position, and means for biasing said member toward its second position.

5. A refrigerator control comprising a pivoted operating arm movable between two positions for starting and stopping refrigeration at predetermined maximum and minimum temperatures, a temperature-responsive element engaging said arm for effecting movement thereof, a biasin spring engaging said arm for opposing said element, a pivoted interfering member movable between a first position wherein said mem ber opposes movement of said arm and a second position wherein said member does not oppose movement of said arm, a latch for engaging said member, said latch including a ho engaging one side of said member, a cam engaging said latch for affording movement of said latch to shift said member to its first position, and a sprin engaging the opposite side of said member for biasing said member toward its second position.

6. A refrigerator control comprising a pivoted operating arm movable between two positions for starting and stop-ping refrigeration at predetermined maximum and minimum temperatures, a temperature-responsive element engaging; said arm for effecting movement thereof, a biasing spring engaging said arm for opposing element, an elongated pivoted interfering member movable between a first position wherein member opposes movement of said arm and a second position wherein said member does not oppose movement of said arm, a latch for engaging said member, a cam engaging said latch for affording movement of said latch to shift said member to its first position, means for biasing said member toward its second position, said temporature-responsive element being adapted to effect longitudinal movement of said member when said member is in said first position, and a defrost spring for opposing said longitudinal movement of said member.

7. A refrigerator control comprising a pivoted operating arm movable between two positions for starting and stopping refrigeration at predetermined maximum and minimum temperatures, a temperatureresponsive element engaging said arm for effecting movement thereof, a biasing spring engaging said arm for opposing element, a pivoted interfering member movable between a first position wherein said member opposes movement of said arm and a second position wherein said member does not oppose movement of said arm, a resilient latch, said latch including a hook for engaging said member, said resilient latch being arranged to bias said member to its first position when said hook is in engagement with said member, a cam for affording movement of said latch by its resilience to shift said member to its first position, and means for biasing said member toward its second position.

8. A. refrigerator control comprising a pivoted operating arm movable between two positions for starting and stopping refrigeration at predetermined maximum and minimum temperatures, a temperature-responsive element engaging said arm for effecting movement thereof, a biasing spring engaging said arm for opposing said element, a pivoted interfering member movable between a first position wherein said member opposes movement of said arm and a second position wherein said member does not oppose movement of said arm, a stop for limiting movement of said member toward said second position, a latch for engaging said member, said latch including a hook engaging one side of said member, a cam engaging said latch for affording movement of said latch to shift said member to its first position, and a spring engaging the opposite side of said member for biasing said member toward its second position.

Q. A refrigerator control comprising a piveted operating arm movable between two positions for starting and stopping refrigeration at predetermined maximum and minimum temperatures, a temperature-responsive element engaging said arm for effecting movement thereof, a biasing spring engaging said arm for opposing said element, a pivoted interfering member movable between a first position wherein said member oppo es movement of said arm and second position wherein said member does not oppose movement of said arm, a stop for limiting movement of said member toward its first position, a second stop for limiting movement of said member toward its second position, a latch for engaging said member, said latch including a hook engaging one side of said member, a cam engaging said latch for affording movement of said latch to shift said member to its first position, and a spring engaging the opposite side of said member for biasing said member toward its second position.

10. A refrigerator control comprising a pivo'ted operating arm movable between two positions for starting and stopping refrigeration at predetermined maximum and minimum temperatures, a temperature-responsive element engaging said arm for effecting movement thereof, a biasing spring engaging said arm for onposing element, a pivoted interfering member movable between a first position wherein said member opposes movement of said arm and a second position wherein said member does not oppose movement of said arm, a stationary bracket having an opening therein, said pivoted member extending through said opening, said pivoted member engaging one edge of said opening for limiting pivotal movement of said member toward its first position and engaging another edge of said opening for limiting pivotal movement of said member toward its second position, a latch for engaging said member, said latch including a hook engaging one side of said member, a cam engaging said latch for affording movement of said latch to shift said member to its first position, and a spring engaging the opposite side of said member for biasing said member toward its second position.

11. A. refrigerator control comprising a pivoted operating arm movable between two positions for starting and stopping refrigeration at predetermined maximum and minimum temperatures, a temperature-responsive element engag ing said arm for effecting movement thereof, a biasing spring engaging said arm for opposing said element, a pivoted interfering member movable between a first position wherein said member opposes movement of said arm and a second position wherein said member does not oppose movement of said arm, a latch for engaging said member, said latch including a hook engaging one side of said member, a cam having a surface for progressively moving said latch through said opening, said cam surface being arranged for affording abrupt retraction of said latch for moving said member to its first position after said hook has engaged said one side of said member, and a spring engaging the opposite side of said member for biasing said member toward its second position.

12. A refrigerator control comprising a pivoted operating arm movable between two positions for starting and stopping refrigeration at pre-- determined maximum and minimum temperatures, a temperature-responsive element engaging said arm for effecting movement thereof, a biasing spring engaging said arm for opposing said element, an elongated pivoted interfering member movable between a first position wherein said member opposes movement of said arm and a second position wherein said member does not oppose movement of said arm, a latch for engaging said member, said member having an opening therein, said latch being adapted to extend through said opening, said latch including a hook for engaging said member, a cam engaging said latch for affording movement of said latch to shift said member to its first position, i

said temperature-responsive element being arranged to effect longitudinal movement of said member when said member is in its first position, a defrost spring for opposing said longitudinal movement of said member, and means for biasing said member to shift said member to its second position when said member has been moved longitudinally sufliciently to align said hook with said opening.

13. A refrigerator control comprising a pivoted operating arm movable between two positions for starting and stopping refrigeration at predetermined maximum and minimum temperatures, a temperature-responsive element engaging said arm for effecting movement thereof, a biasing spring engaging said arm for opposing said element, an elongated pivoted interfering member movable between a first position wherein said member opposes movement of said arm and a second position wherein said member does not oppose movement of said arm, a stationary bracket having an opening therein, said member extending through said opening, said pivoted member engaging one edge of said opening for limiting pivotal movement of said member toward its first position and engaging another edge of said opening for limiting pivotal movement of said member toward its second position, a latch for engaging said member, said member having an opening therein, said latch being adapted to extend through said opening, said latch including a hook for engaging said member, a cam engaging said latch for affording movement of said latch to shift said member to its first position, said temperature-responsive element being adapted to effect longitudinal movement of said member when said member is in its first position, a defrost spring for opposing said longitudinal movement of said member, said bracket including a stop for engaging said latch to limit movement of said hook in a direction toward said defrost spring, and means for biasing said member to shift said member to its second position when said member has been moved longitudinally sufliciently to align said hook with said opening.

CHARLES S. GRIMSHAW.

References Cited in the file 01 this patent UNITED STATES PATENTS Number Name I Date 1,867,711 Raney July 19, 1932 1,933,589 Bauer Nov. '7, 1933 2,093,835 Grooms Sept. 21, 1937 2,125,070 Grooms July 26, 1938 2,137,728 Raney Nov. 22, 1938 2,376,913 Grooms May 29, 1945 2,459,083 McCloy Jan. 11, 1949 2,584,482 McCabe Feb. 5, 1952 

